Complex, ritualized behaviors can be programmed into animals by the action of genes. It is proposed to dissect this genetic programming by studying reproduction in Drosophila melanogaster. First, it will be determined which portions of the nervous system must be genetically male to allow the various stages of male courtship to be performed. The procedures here involve observations on the behavior of genetic mosaics, followed by the histochemical scoring of the genotypes of different parts of the head and thoracic ganglia. There are mutants which appear specifically to disrupt male courtship, possibly by affecting nervous system stages: with respect to initial "preference" for courting females vs. males: with respect to a later step, attempted copulation of females; and with respect to the timing of copulation duration. These mutants will be (1) characterized in a preliminary fashion, both genetically and behaviorally, (2) analyzed by manipulation of their courtship environment, and (3) analyzed by mosaic techniques, to see which part (if any part) of the nervous system they affect. Isolation of additional courtship mutations is proposed, which will hopefully affect other steps in the sequence. The genetic, behavioral, and mosaic characterization of courtship mutants will pave the way for an understanding of the mechanism of the mutant defects, involved in the programming of courtship behavior. BIBLIOGRAPHIC REFERENCE: Kankel, D.R., and H.C. Hall. 1975. Fate mapping of nervous system and other internal tissues in genetic mosaics of Drosophila melanogaster. Devel. Biol., accepted for publication and in press.